Soviet nuclear science and technology
made great achievements before the Second World War. But War (1941 - 1945)
completely stopped all Soviet studies in this field. However during this
period scientists in the USA and England made revolutionary progress in
investigation of the applications of nuclear fission. Unfortunately this
progress was initially used for military purposes. The end of Second World
War was marked by use of nuclear weapons against Japan. The mere possession
of nuclear weapons enabled the USA to exert enormous international pressure
and led the government of the USSR to try to "balance the power". A special
committee was established by the State Committee for Defense (Resolution
number 9887 dated 20th August 1945) for the production of nuclear
weapons, with an unprecedented sense of urgency: the "Uranium Project"
(1,2).

Fig 1. Location
of the first Soviet plutonium production plant: "Mayak" Production Association

The Uranium Project in the USSR
was implemented under great economic difficulties, with a dearth of skilled
scientific and technical specialists and material resources. Butthe results were achieved in a short time. Two experimental design
facilities were established in Kirovís Factory in Leningrad ( now St.Petersburg).
The first equipment was designed for uranium isotope enrichment by gaseous
diffusion, the second was a laboratory for the development of heavy-water
reactors fuelled by natural uranium; and the construction of two plants
for the uranium enrichment and plutonium production respectively were started.
The second of these plants was the first Soviet plant for weapon-grade
plutonium production and was located in the Southern Urals (Fig.1). Igor
Kurchatov was appointed Scientific Leader of this facility. A site in the
Ural Mountains was chosen as the best place for the constructionbecause
of the convenient and safe position in the middle of the country far from
the borders of the USSR (and at the time inaccessible for raiding aircraft
from beyond the borders), yet close to necessary resources and communications.
In the summer of 1945 the site selection survey was made, and in autumn
of 1945 the government commission decided to construct the first of seven
military reactors on the southern shore of Lake Kyzyltash. Soon, a number
of auxiliary enterprises were set up, and they were connected by
network of roads, power and water supply communications. Houses for the
employees of the enterprises were built nearby. It was the industrial complex,
which is known now as "Mayak" Production Association (1,2). Originally
a closed city called only by its postal code (Chelyabinsk-40, Chelyabinsk-65),
the city was given the name of Ozersk in 1994.

The main purpose of the "Uranium
Project" was the creation of Soviet nuclear weapons as fast as possible.
By the end of 1947 the first military reactor (A-plant) was ready to operate.
The reactor was started on 8th of June 1948 and by 19th June
1948 it had reached the designed power (100 MW). It had been operating
for plutonium production for 39 y when it was shut down on 16 June 1987.
Three additional reactors were put into operation in the period 1950-1952
have also been shut down. All these four reactors were graphite-moderated
reactors with direct water cooling loops, using cooling water from the
lake Kyzyltash. Only two reactors of the seven built during the operation
of the Mayak are still working for civilian needs (1). The radiochemical
plant (plant B) for extraction of 239Pu from uranium irradiated
in the reactor of the A-plant was put into operation in December of 1948.
And in February of 1949 the first plutonium concentrate from the plant-B
was converted to high-purity metallic plutonium for the first Soviet atomic
bomb at the metallurgical plant (V-plant).

In the 1950s nuclear technology
was not yet well developed and there was not enough knowledge in the world
and still less in the USSR about the fate of radioactive wastes in natural
ecosystems and the effects of radiation on humans. Therefore, efforts to
prevent discharges of radioactivity into the environment were insufficient,
and territories in the vicinity of Mayak were severely contaminated by
radionuclides, including long lived 137Cs and 90Sr
.

In the first years of the Mayak
operation there were three accidents accompanied by large releases of radioactivity
in the environment (1-4):

1. Techa River contamination (1949-1956,
~ 100 PBq);

2.Kyshtym
accident (1957, ~70 PBq)

3.An
incident with dispersion of radioactive dust (1967, ~20 TBq).

Soon after the start of the Mayak
plant, the problem of storage of radioactive wastes of the radiochemical
plant arose. The usual way that radioactive wastes in the first years of
the Mayak operation were managed was to dump low-contaminated wastes directly
to the Techa River system (some of them were passed through the absorbers).
This was the practice in the period 1949-1956. Highly contaminated wastes
were directed to the tank farms of a special storage facility (complex-C).
In January of 1950 a special facility for the decontamination of high-level
radioactive wastes was built, and the construction of additional tank farms
at complex-C was stopped. Unfortunately, it was found soon that the decontaminating
facility did not operate as intended, and this failure resulted in an increase
of radioactive releasers in the Techa River. In addition the tanks of complex-C
had to be cooled constantly to prevent self-overheating of wastes that
contained high-levels of chemicals and radioactive materials. Eventually
some leakage occurred through imperfections in the cooling system. Since
the water from the Techa River was used as the cooling agent in this system,
large amounts of radionuclides (with the daily mean of 0.16 PBq) were eventually
discharged into the river in the period 1950-1951. As a result appreciable
quantities of radioactivity accumulated in the water and bottom sediments
of the river, especially in the upper reaches. In October of 1951 the discharge
of radioactive materials into the Techa was reduced and the wastes were
collected in an enclosed artificial reservoir known now as the Lake Karachay.
Later, arrangements were made to close the Upper Techa and prevent future
dissipation of radionuclides deposited there.

The Techa River contamination was
the most serious "accident" but was not the last one. In 1957 the cooling
system of one of the storage tanks containing highly radioactive liquid
wastes failed to operate properly and the tank overheated and exploded
(Kyshtym explosion; 1,4). This tank contained 70,000-80,000 kg of wastes
mainly in the form of nitrate compounds. Energy released by radioactive
decay caused a daily temperature increase of 50C to 60C.
The temperature was controlled using cooling water, which was completely
replaced every 12 h. Apparently, the cooling process and temperature control
system for the exploded tank failed, the temperature of the waste increased
to 330-3500C and the cooling water completely evaporated. On
the 29 September 1957 the tank exploded. About 90% of the radioactive material
contained in the tank (700 PBq) was deposited close to the site of the
explosion, but the rest (about 70 PBq) formed a radioactive cloud, which
reached a height of about 1 km, and drifted with the wind to the north-north-east
direction, forming the new contaminated territory. This contamination site
known now as East Urals Radioactive Trace (EURT). It covers about 15,000-20,000
km2 territory, with approximately 5% (about 1,000 km2)
with initial radionuclide densities greater than 70 GBq/km2
(1).

Finally in 1967 there was little
snow and the spring and summer were hot and dry. Evaporation reduced the
level of water in the Karachay Lake dramatically, and the radioactive dust
from the bare banks was spread by wind over surrounding territories. About
1800 km2 were contaminated at the levels 1-10 GBq/km2,
and the contamination reached 50-70 km from the Mayak site. By 1967 the
residents of territories near the Karachay lake had been resettled.

In spite of military secrecy, the
fact that a severe accident had occurred was known in the west as early
as 1961. The general outlines of the Kyshtym explosion was deduced by American
scientists about 1975 (4) but no details were known. In 1990 the scientific
research related to these accidents were declassified, and the first public
articles appeared in Priroda (5) The number of scientific publications
about radioactive contamination in Southern Urals, and particularly about
the Techa River contamination, is rapidly growing . The purpose of this
review is to collect the information about the Techa River accident and
related investigations and make it more accessible to a wider range of
readers. The Techa River accident was selected by two reasons: 1) it was
the most significant accident in the region with the largest number of
people exposed at levels of radiation of more than 0.05 Sv; 2) the current
state of this case study is more advanced than the study of the other accidents,
and 3) a statistically significant radiation impact on the population was
detected.

The Techa River contamination

Location
and hydrological characteristics

The Techa River is the right tributary
of the Iset River. It belongs to the basin of the Kara Sea (Fig. 1). The
sources of the river are the Irtyash and Kyzyl-Tash Lakes. It falls into
the Iset River, which in turn falls into the Tobol River. The length of
the river is about 240 km. At the time of the radioactive pollution there
were 40 villages on the river with a resident population about 28,000 (Fig.
2). These were mostly small agricultural villages. Brodokalmak village
was the center of the administrative region

Fig. 2. Map of the Techa River and of
the villages located on its banks before contamination occurred. The number
of residents, their ethnicity and current status (evacuated or not) are
also shown. Total population in 1950 was 27454 (reproduction from (37)).

The riverbed includes layers of
turf, silt and clay. There were flood swamps which measured 300 m to 2
km in width along the river shoreline; the most swampy areas were located
between the villages of Nadyrov Most and Muslyumovo. The flood soils were
composed of turf-bog soils that give way to meadow-turf ones along the
boundaries of the swamps. The thickness of the turf layer ranges from 10
cm to 3 m, the turf contains a considerable amount of mineral inclusions
and increased percentage of ash. Clay and sandy loam, less frequently sand,
compose the underlying layer of turf.

Downstream of the village of Muslyumovo
the river has a well-formed bed (Fig.3), its bottom consists of layers
of sand and slime, in some places of sand and gravel. The mean width and
depth of the river during the summer time are 22 m and 0.5 m to 1 m, respectively.
The stretches of the river from Kyzyl-Tash Likes to the village of Muslyumovo
were for the most part swampy with a poorly marked winding bed overgrown
with water plants. The width of the riverbed varied from 3m to 15m and
its depth ranged from 0.5m to 2 m.

The Techa River receives its supply
of water from melting snow and intensive spring floods. The main source
of water supply to the Techa during the summer months is discharge from
groundwater formed by atmospheric precipitation. In the 1950s the flow
rate varied from 2 m3/s to 10m3/s. The Techa river
is rather small and shallow. That was one of the reasons that there was
appreciable contamination of the river environs.

Fig. 3. Techa river near the Nizhnepetropavlovskoye
village (148km downstream the site of releases) with the houses in the
background

As shown in fig. 4, in the upper
reaches of the Techa there is now a cascade of hydraulic-engineering constructions
(6).

a)

b)

c)

d)

Fig. 4. Schematic maps of the upper reaches
of the Techa:

a)At the beginning of "Mayak" PA operation;
b) After creation of the Koksharov Pond; c) After creation of reservoir
No 10; d) After the upper reaches are made a "closed system". The main
sources of contamination were liquid radioactive wastes from the radiochemical
plant and reactor cooling water dumped into the Kyzyl-Tash Lake. Two other
radiation accidents gave a minor contribution to the Techa River contamination
also (Kyshtym accident producing the EURT and Dust Transfer from the banks
of Karachay Lake) (reproduced from (6)).

Only the Metlinsky pond existed
when Mayak began operation. Later, in 1951 the Koksharov Pond was created
to prevent direct flow of radionuclides to the Metlino village (Fig 5).
It was the first village downstream 7 km from the point of the releases,
and the residents accumulated the highest radiation doses there. In 1956
arrangements were started to restrict the influence and spread of radioactive
contamination: residents of upper reaches of the river were evacuated and
a series of additional dams were built (Fig.4).

Fig. 5. Metlino village was situated
7km downstream of the site of releases of liquid radioactive wastes by
"Mayak" plant, before the evacuation of residents in 1951. Later almost
all buildings were destroyed, although the buildings seen at this picture
(the church and the mill) remain. They are used now for collection of brick
samples for thermoluminescent dosimetry measurements (18-20). The water
reservoir at the foreground is the reservoir N10 created in 1956. Now the
buildings are still decaying by natural processes. Metlinsky pond is situated
behind the mill buildings. (The picture by E.I.Belova is presented from
personal archives of Dr. Nelli Safrnova with her permission)

Mayak
as a source of Techa contamination

The production of weapons-grade
plutonium at Mayak required a number of stages. At the first stage the
natural uranium was irradiated in the uranium-graphite reactors with thermal
neutrons to generate 239Pu in the fuel at the reactor complex-A.
After irradiation the fuel was treated at the plant-B to separate of the
239Pu from natural uranium. Then the product enriched by 239Pu
was directed to the metallurgical plant-V to produce high-purity metallic
plutonium (1,6).

There were a number of sources
in this chain that contaminated the Techa River. The reactors in the complex
A contained only one cooling loop: the water from Kyzyltash Lake circulated
directly through the reactor core and released back to the lake. As a result
cooling water contained radionuclides with short half-decay times generated
by irradiation of material in the active zone of reactor. The water from
the contaminated lake was one, but not the main, source of Techa River
pollution. There were various kinds of waste products after extraction
of uranium and plutonium from the irradiated fuel at the radiochemical
plant B. Liquid radioactive wastes with intermediate and low-level radioactivity
were dumped directly to the Techa River. In 1949 high-level wastes were
routed to the tank farms in the complex-C. However in order to reduce the
volume of materials going to the tanks, a process for decontamination of
high-level wastes was introduced in 1950 with a portion of the radioactivity
directed to the tanks and a portion released to the river (6). In July
1951 it was discovered that this process did not work as intended, and
during this period large quantities of radionuclides had been released
into the river. It was also noted that sometimes cooling water from
the tanks of Complex C was discharged into the Techa.

Leaks in the tank- cooling lines
caused some of these discharges to be highly contaminated. These "wild
releases" were unmonitored and unnoticed until 1951. Over this period,
about half of the total release to the Techa River resulted from routine
releases and about half from wild releases (6).

The nature and quantity of the
released radionuclides in 1950-1952 were estimated by Ilyin in his Doctoral
Thesis (7,6), the head of the Mayak Central Laboratory. These estimates
were made on the basis of all available measurements and with knowledge
of technological processes at Mayak. Later (1953-1956) similar estimates
were made by Marey (8) in his doctoral thesis using the results of measurements
by special expeditions under the supervision of Moscow Institute of Biophysics.
The sources of information used by Ilyin and Marey as well as their original
reports as of 1999 are still classified. They estimated that about 100
PBq of beta-emitters were released into the Techa river, and approximately
98% of this total activity was dumped in the period March 1950 to November
1951. The total amount of gamma-emitters was as much as 24% of the released
beta activity, and the released activity of alpha-emitters was less than
2 TBq. About 70% of released activity were incorporated in solid particles
of sodium nitrate and acetate. The estimated average daily releases and
their approximate radionuclide composition are presented in table 1.

Table 1. Estimates of nature and
quantity of radionuclide releases into the Techa River in earlier period
of operation of the Mayak plant. Based upon Ilyin (7) and Marey (8).

Year

Release,
TBq/d

90Sr+89Sr

%

137Cs

%

Rare
Earths

103,106Ru

%

95Zr+95Nb

%

1949

2.6

5

10

-

55

30

1950until
March

32.2

15

15

6

45

9

March 1950 to Sept 1951

161

21

12

27

26

14

1951
since October

3.74)

26-58*

4-15*

10-61*

-

8-25*

1952

0.9

26-58*

4-15*

10-61*

-

8-25*

1953

0.74

26-58*

4-15*

10-61*

-

8-25*

1954

0.56

44

10

45

1

*Only
range estimation is available.

Note: the data
were originally presented with excessive precision, but their sum sometimes
is not equal to 100% . Therefore they are rounded in this table, to emphasize
that the estimation is approximate.

As shown in table 1, in the period
of 1952-1955, the releases of the radiochemical plant were much reduced.

Another significant source of contamination
was the reactor cooling water that flowed into the Techa River from Kyzyl-Tash
Lake. For example, during seven months in 1953, the activity released from
the reactor was five times the release from the radiochemical plant (6).
The water of Kyzyl-Tash Lake entering the Techa was also contaminated by
the activation radionuclides 32P, 35S, and 45Ca.
The ultimate fate of radionuclides in the river system was determined by
a number of parameters including radioactive decay; transport and dilution
by water flow; sedimentation of particulate fraction of the releases; and
absorption and desorption processes in soluble fraction of releases with
participation of particles of natural admixtures in the water with consequent
sedimentation of these particles (9-10).

The nature of the releases, the
resettlement arrangements in the Upper Reaches, the specific transport
processes and the transport features of specific radionuclides determined
the following pattern of the contamination (1,3,6,9,10,11,12). The radioactivity
decreased fast with calendar year since 1951, and with distance from Mayak.
The short-lived radionuclides and the radionuclides in particulate form
decayed or settled almost totally in the Koksharov and Metlinsky ponds.
In the rest of the river the main contaminants were 137Cs and
90Sr.

Since 1964 the river was effectively
in a self-cleaning regime, accompanied by the slow decay of 137Cs
and 90Sr. The radioactivity was accumulated predominantly in
river bottom sediments: the ratio of concentrations in bottom sediments
to water concentration varies in the 100-1000 fold depending on the nature
of the sediments. Flood plain soils were contaminated during spring floods,
especially during the outstanding flood of spring 1951. Houses and land
were contaminated due to the activity of people and agricultural animals.

Regular environmental measurements
were started in the summer of 1951 when the mistakes in the treatment of
radioactive waste became evident (3,6). The most representative measurements
(almost daily at a representative set of locations) were made for the total
beta activity of river water. Eventually samples of river sediments and
flood plain soils were collected at different locations along the river
and a number of radiation dose-rate measurements were made in air near
the river edge, in the streets of the villages and in houses. One of main
purpose of these measurements was the determination of critical groups
of the population - those who accumulated large doses - in order to make
decisions about their evacuation from contaminated territories. That goal
did not require systematic and precise monitoring and attention was centered
on high-level values. This approach has added difficulties in the reconstruction
of radiation doses of the exposed people.

The radionuclide concentrations
decreased 10 fold in water and radioactive concentrations in the bottom
sediment decreased 100-1000 fold from the upper reaches to the mouth (Fig
6).

Fig. 6. The results of measurements of
total radionuclide concentration in river water and bottom sediments in
1951 and 1953. The radioactivity of the water decreased approximately 10
fold along the river. The units of the y axis are different for each line
and are shown in the inset describing each line. Data are taken
from Vorobia et al. (6)).

The dilution by clean water of
the Iset River caused an additional 10-fold decrease. And there was further
100-1000 fold dilution in the Tobol River (3). Thus the contamination of
Iset and Tobol Rivers can be considered to be comparatively insignificant.
The most significant radiation conditions were in the upper and middle
Techa.

In 1951 the level of pollution
of water in the Metlinsky Pond (Fig. 4a, 5) allowable levels for 90Sr
exceeded by 2,000 to 3, 000 and the 137Cs level exceeded 100
times (3). The radiation exposure rate reached in some places the levels
at which in only one hour a person could have accumulated a radiation dose
comparable with the maximum annual allowable dose for radiation workers.
Since late 1951, when the massive releases ceased, there was about 100-fold
decrease in exposure rates (3). However in the subsequent period the exposure
decreased slowly due to slow decay of cesium in the coastal strip of the
river.

Population Protection Measures

The elevated radiation levels in the
Upper Reaches of the Techa in 1950-1952 were of concern to the health of
local inhabitants, particularly because they used the river as the basic
and often sole water supply resource. The situation required a set of measures
to protect people's health (3).

Effective from the autumn of 1951
it was officially forbidden to use the river for drinking, swimming, domestic
and agricultural needs. Then the migration of residents of the village
of Metlino began. Despite the reduction in the releases the concentrations
of radionuclides still exceeded allowable levels. For this reason a new
dam was built on the swampy area downstream of the Metlino village (Fig.
4c), which was constructed in 1956. However a significant reduction was
not achieved. By that time the main source of pollution of water was releases
of radionuclides from bottom sediments. Therefore, it was decided to construct
additional dams and canals, which totally isolated the hydraulic engineering
objects of Mayak and the polluted marshes in Upper Techa River from the
rest of the Techa in 1963 (Fig. 4d).

During this period a set of additional
administrative measures were taken about the territories along the Techa
River. A number of riverside fields covering about 80 km2 were
forbidden for agricultural uses (3), the riverside territories were fenced
by barbed wire and warning signs were set up. Special security guards were
organized to enforce these measures. Water pipes and wells were constructed
for maintenance of drinking and economic water supply. The use of the water
of the Iset River for drinking and fishing was forbidden (3). These measures
decreased the levels of irradiation of the population. Meanwhile the resettling
of the residents was extended, and by 1960 about 7500 residents had been
resettled (3) (Fig.2).

Radiation Doses of the Population

The reconstruction of doses to
the population that were exposed is always a difficult task. Because of
its importance the way in which dose to one individual was estimated is
described in some detail. At the Techa River people were irradiated both
internally and externally. The reconstruction of the internal dose (mainly
due to 90Sr) is more important for the largest part of the population,
and it is more reliable than the estimation of the external dose.

The external gamma-irradiation
was predominant only for those who lived in the Upper Reaches of the Techa
in 1950-1952 and consumed relatively small amount of water from the river.
The main cause of external irradiation was gamma-irradiation by 137Ba
, the decay product of 137Cs. The 137Cs was mainly
accumulated in bottom sediments. The important factors determining the
level of external irradiation were the dose rate in air near the river
where the inhabitants spent daily. Some additional irradiation occurred
in streets of the villages, which were contaminated via human activity,
and inside houses due to usage of river water for domestic activity.

Except for the residents of upper
Techa the main pathway of dose accumulation for riverside individuals was
internal irradiation by beta particles of ingested 90Sr and
137Cs (11,12). Cesium did not give a large contribution to internal
irradiation for two reasons: it accumulates in organ tissues uniformly,
and it has a comparatively short retention time in an organism (about 100
d for an adult). The contribution of 90Sr (including its decay
product 90Y) to the internal dose was more significant because
it is concentrated in human bone tissues for a relatively long time. The
largest doses of internal irradiation were accumulated by those who were
teen-agers in the 1950's: their skeletons were growing rapidly requiring
the largest amounts of calcium and hence, the 90Sr (11,12).
The main source of ingested strontium in 1950-1951 was drinking water from
the river. Later, after the wells and pipes construction and prohibition
of usage of the river water, the main source of radionuclides intake was
the milk from cows pastured in the contaminated territories.

These estimations for external
irradiation are based on: 1) average values of the dose rate measured near
the river bed, on the streets of the villages and in the houses; and 2)
a survey by M. Saurov (Moscow Biophysics Institute), who estimated the
mean times spent at the river by residents of the different age-cohorts
in the 1950's (11, 12)

The data available do not provide
information on the variations in individual dose levels between the residents
of a village. Instead the average value for specified age groups and specified
settlement is assigned to each resident. In this approach the personal
variability of the external dose is described only by the variability in
personal residence histories.

A possible method for dose reconstruction
consists of measurement of the number of Electron Paramagnetic (Spectral)
Resonance centers (ESR) in natural crystals contained in tooth enamel and
cement and in other bone tissues. This number is proportional to the dose
of external irradiation accumulated by a person (13-17). However, these
measurements are difficult and expensive and not many of them have yet
been made for the Techa residents. Additional verification of the levels
of external exposure can be made now using Thermolumeniscent Dosimetry
(TLD), using the ability of some natural minerals. A number of such measurements
were made using brick samples taken from buildings of Metlino and Muslyumovo
villages to validate estimations of external exposure in the 1950's. They
are in reasonable agreement with calculations as well (18-20).

In the late 1950s special branch
N4 of Moscow Biophysics Institute (now called Ural Research Center for
Radiation Medicine: URCRM) was organized in Chelyabinsk city (Fig. 1).
Its purpose was to control the health status of the population irradiated
as the result of Techa River contamination and (later) the Kyshtym accident
of 1957. A 90Sr whole-body counter (WBC SICH-9.1) was designed
there in 1974 (21). Because neither the 90Sr nor its daughter
90Y emit gamma rays WBC SICH-9.1 was designed to measure bremsstrahlung
resulting from beta emissions. WBC SICH-9.1 could measure the content of
the 90Sr and 137Cs separately using specific features
of their photon spectra (21).

The WBC SICH-9.1 is a big metal
tube (shielding room), with four photon detectors connected to a computerized
analyzer. The detectors were fixed in the central vertical plane of the
shielding room. On the bed frame a fabric is placed which stretches under
the weight of the body in such a way that the medium plane of the body
is at equal distances from each detector. During measurement the person
lying on the bed is moved through the detector array. The motion is controlled
by signals from the analyzerís real-time clock. The measurements are made
during controlled stops of the bed (21). Calibration of the WBC SICH-9.1
was carried out in 1974 using phantoms designed in two different laboratories
(21). The difference in the calibration coefficients from different laboratories
was about 10%.

The WBC SICH-9.1 measurement provides
the radioactivity content of the body at the time of measurement and does
not give the desired accumulated radiation dose. To calculate the total
dose absorbed by tissues during the whole period of irradiation, one should
know the dose-rate at each moment of the irradiation time for integration
over time. Unfortunately, there were no WBC SICH-9.1 measurements before
1974, and when they were started the period of high radionuclide body burdens
for the exposed peoples was in the past. Thus the dose must be reconstructed
using a mathematical model, which describes the radionuclide content in
human tissues depending on time (22-26). An example of such a calculation
is shown in Fig.7. Moreover the WBC SICH 9.1 measurements are available
only for part of the exposed population. For the rest of the population
a Reference Model is used, which represents the average 90Sr
content for the group of people exposed at given age at a fixed location.
If individual measurements are present we can adjust the Reference Model,
multiplying it by a factor, which provides the best fit of the model predictions
for the individual body burden (Fig.7). This adjustment is based on the
assumption that the temporal pattern of radionuclide intake for the given
person was the same, as for the "reference person", but the value of intake
was greater (or less) with the factor, described above, due to specific
personal behavior or residence location. The main reason for variability
of radionuclide intakes between persons was the presence or absence of
wells with clean water.

Fig. 7. Example of the reconstruction
of strontium-90 body burden. The lower dashed line represents the Reference
Model describing the average body burden for the residents of the Techa
of the same age and residence history as for the person with individual
code 65737. The upper curve represents the model, adjusted to represent
the individual Whole Body Counter (WBC) measurements for this person: the
adjustment factor is equal 5.97 in this case (WBC data are reproduced with
permission by E.Tolstikh, private communications).

The Reference Model is used for persons with absence of individual measurements.
1kBq corresponds to 1000 radioactive decays per second in the skeleton.
Each of these decays gives its contribution to accumulated dose. Thus reference
and individual accumulated doses are proportional to the square of the
areas under the corresponding solid lines. In the shown extreme case the
individual dose is greater than the reference dose, but the opposite situation
can take place for other persons, and in the average value of individual
correction factor is equal to 1.

An additional difficulty was that
the mathematical model required information about the dynamics of radionuclide
intake for the given person or for a group of persons.

It is possible to determine the
intake of 90Sr using measurements on each person's teeth (23).
The teeth enamel is formed only in the first years of life Therefore, the
measured radioactive decay is almost entirely from the 90Sr
that entered the enamel in childhood. The 90Sr content in the
enamel can be determined using conventional beta counting using one and
the same procedure.

Absolute values of the intake could
be obtained using the more precise WBC SICH-9.1 measurements. Given the
time-pattern of the intake for 90Sr, and using estimated ratios
of concentration of other radionuclides in food relative to 90Sr,
it was possible to estimate the intake of other radionuclides. At present,
it was assumed that these ratios were the same as the corresponding radionuclide
concentration ratios in the river water for given time period and location.
Given the intakes, and using model curves analogous to those shown in Fig.7
but for other radionuclides, it was possible to estimate the contribution
of all spectra of ingested radionuclides (Fig. 8).

Fig.9. The radiation dose accumulated
in the Red Bone Marrow for permanent residents of the Techa riverside.
The "Reference Model" is used for all members of the Techa River Cohort.
Effective dose equivalent limit for continuous exposure for public during
50 years is equal to 0.05 Sv (5 rem) (26).

It is clear from the above considerations
that it is impossible to base the dose assessment for the population using
only direct measurements. They must be accomplished by calculations with
mathematical models fitted to data. In order to use the mathematical model
for individuals based on their residence histories the Techa River Dosimetry
System (TRDS) code was created. For a better understanding of the scheme
of the dose calculation with TRDS the calculation process is described
for the red bone marrow dose for a particular person (code number 65737).

A database MAN was created in the
URCRM to support the follow-up of exposed peoples. In particular, it contains
information about person's residence history, which is used for individual
dose calculations. Each exposed person has a "system number" used as an
identification code. The person with the system number 65737 was born in
1928 in the Ibragimovo village (Fig.2). In 1953 he moved to the Muslyumovo
village where he died in 1995. The selected person was exposed in two locations
during the period of 1950 to1955, when external exposure and radionuclide
intakes were significant. The total period of dose accumulation was 45
y.

The radiation dose is calculated
in the TRDS according to the following formula

(1)

where

Do
= cumulative dose to organ o;

m
= month of exposure;

L(m)
= place of residence for the mth month (river location identifier);

r
= radionuclide identifier;

Age(m)
= the age of the person in the mth month;

RISr-90 (Age(m),L(m))=
reference intake of 90Sr for given time and location

fr(m,L(m))
= fraction of r-th radionuclide in river water relative
to 90Sr;

DFro(Age(m))
= dose factor for radionuclide r in organ o;

p
= place of exposure identificator (indoor, outdoor, at the river bank)

DRp(month,L(month))
= dose rate in air

Ao(Age(m))
= air-to-organ correction, independent of energy (Sv/Gy)

Tp
= time spent at the given place of exposure

The reference intake of 90Sr
in 1950 in the Ibragimovo village, obtained from teeth beta-counting in
(21) as described above, was about 2 MBq. The person 65737 resided in Ibragimovo
throughout the whole of 1950. There are two options: 1) use the "Reference
Model" for the intakes for the whole population; and 2) use the individual
model, based on WBC measurements. The first approach is appropriate if
we want to know the doses for the largest number of people, who can have
no WBC SICH-9.1 measurements, the second one can be applied for selected
sub-cohort of peoples with known WBC SICH-9.1 measurements. These two approaches
should not be mixed for biasing reasons: persons with the highest doses
have the higher probability to have WBC SICH-9.1 measurements which are
available for selected persons. They are shown in Fig.7. The ratio of the
reference and the adjusted 90Sr content for this person is about
6. If the individual approach is used, the reference intake of 2 MBq must
be multiplied by 6 resulting in 12 MBq. The reference intakes of other
radionuclides, are calculated from 90Sr reference intake RISr-90
and radionuclide fraction in river water fr (Eq.1),
using the model of radionuclide transport in the river (9) resulting in
1500 kBq of 89Sr, 1000 kBq of
137Cs, 300 kBq of 103Ru,
1500 kBq of 106Ru , 700 kBq of 95Zr, 23 kBq of 95Nb,
0.350 kBq of 141Ce and 87 kBq of 144Ce. These values
were calculated using model of radionuclide transport, the ratios of concentration
of each radionuclide and the 90Sr concentration in river water
for given time period and location. It was assumed that these ratios are
the same, as the analogous ratios of radionuclide concentrations in resident's
diet for this time and location. To use the individual model each of the
listed intake values should be multiplied by 6.

Given the values of the intakes,
the accumulated dose of internal irradiation for the person 65737 can be
calculated using tabulated dose coefficients DFro
values from instant intake of 1 Bq of each radionuclide in 1950, when the
person was 22 y old for subsequent 45 y of exposure. These tables of "dose-coefficients"
are available for the majority of radionuclides in the recommendations
of the National Council on Radiation Protection and Measurements (27,28).
We use the tables calculated on the basis of these recommendations by V.Berkovsky
(29). But for 90Sr and 137Cs the model (22) is used,
which is based on a large number of WBC measurements and therefore takes
account of the specifics of the irradiation on the Techa river better.
The product of the intake values (multiplied by 6) in 1950 and dose coefficients
give the following contributions to the accumulated dose: 0.05 Sv(89Sr),
3 Sv(90Sr), 0.08 Sv(137Cs), 0.0003 Sv(103Ru),
0.0014 Sv(106Ru), 0.002 Sv(95Zr), 0.00003 Sv(95Nb),
0.00000005 Sv(141Ce), 0.0001 Sv(144Ce).

The dose from external irradiation
is calculated as follows. According to the survey in 1950, an adult
person spent about 150 h at the shoreline (river bank), 1410 h in the streets
of the village, about 3960 h inside his house, and the rest of the time
on clean territories far from the river. Using available measurements it
can be shown, that the average ratio of the dose-rate in air in the residence
area to the dose-rate near the shoreline was about 0.035, and the mean
ratio of dose rates in the houses to dose-rate in the street is about 0.5.
The dose rate in air near the riverbank in 1950 at the Ibragimovo village
was about 2.4 Sv/y. This value was obtained by interpolation of actual
measurements carried out in the 1950's (11). To calculate the external
irradiation dose in the red bone marrow, the shielding effect of other
tissues of the organism must be considered. These coefficients of conversion
of dose-rate in air to dose-rate in a target-organ Ao are available
(30). Using these age-dependent conversion coefficients the fraction of
the dose-rate in the red bone marrow of the person 65737 was about 0.73
of the dose-rate of external exposure. The corresponding contributions
of exposure at the river, in the residence area and inside the house were
0.04 Sv, 0.013 Sv and 0.019 Sv respectively. Thus the contribution of the
first year of exposure for the person with the number code 65737 was about
3 Sv. The contribution of internal irradiation to the total organ dose
was about 98%. The main contaminants, 90Sr and 137Cs,
give about 98% of the dose by internal radiation. The above conclusion
applies only to the bone marrow. If one calculates the dose in target-organs
other than red bone marrow, the contribution of 90Sr should
be much smaller.

The contributions of other years to the exposure are calculated in the
same way, but using values of the intakes, dose coefficients, exposure
rates and behavior specific for the given location, calendar year and current
age of the person. The difference is only in account of the contribution
of the year 1953, when the person moved to the new location. There is no
information on the exact date of this migration for this selected person.
Therefore, it was assumed, that the migration took place in the middle
of the year. Actually the contribution of the year 1953 is the sum of half-year
contribution of residence in the Ibragimovo village, and half-year contribution
of residence in the Muslyumovo village. The contributions of the 1954 and
1955 years are calculated using intakes and the exposure rates corresponding
to the Muslyumovo for these calendar years.

The dynamics of accumulated red
bone marrow dose for the person 65737, calculated in the described way,
and the structure of this dose is shown in fig. 8. The distribution of
accumulated doses in the exposed population of the Techa river residents,
calculated without taking account of individual WBC measurements, but using
the Reference Model only, is shown in Fig.9. It can be seen that the selected
person has an extremely large dose as compared to the majority of the exposed
population.

It is easy to understand that there
are many shortcomings, uncertain and variable factors in the above calculations.
It is possible to estimate their probabilistic distributions, and calculate
the distribution of accumulated dose for the person 65737 (or any other
person) instead of the average dose. It allows as at least attributing
the error range for each calculated individual dose. This approach is more
informative and reliable, but it is only in progress now for the Techa
River Dosimetry System.

Radiation Effects in the Exposed
Population

There are at least two important
reasons for studying the effects of the radiation exposure on the health
of the exposed population. The first radiation measurements were begun
during the summer of 1951- 2 years after releases of radioactive material
into the Techa had started. In the upper reaches of the river, at the shores
of the Metlinski pond 7 km from the discharge point, gamma background levels
were 5 R/h (0.05 Gy/h) at some sites. These levels were high enough to
initiate a study of radiation pathology among the residents of the riverside
villages. Visiting teams of physicians of Medical-Sanitary Department Number
71 (Chelyabinsk 40) and the Biophysics Institute, USSRís Health Ministry
(Moscow), conducted medical examinations of the population. Visiting examinations
at that time, consisted of interviewing the patients, an assessment of
the patientís health status by pediatrician or internal medicine physician,
gynecological examinations of women, and peripheral blood studies including
counts of all morphological elements. In the summer of 1951 only a few
of the Metlino residents were examined. The task of the next visiting team,
which arrived in the area one year later (1952), was to conduct dynamic
examinations of both members of the Metlino community and residents of
villages located on the Techa downstream of Metlino. The first reports
showed the presence of patients with complaints of easy fatigue, general
weakness, sleeplessness, headaches and dizziness, nausea, reduced memory,
pains in bones, stomach and intestine. Objective symptoms were mainly represented
by impairments of hemopoiesis manifested by leucopenia and trombocytopenia.
It was at that time that the occurrence of chronic radiation sickness
was proposed among the exposed population. Later on the studies allow the
observation of such effects of irradiation as increased leukemia and solid
cancer cases rate among exposed peoples and possible genetic effects (late
effects).

Chronic Radiation
Sickness

The concept of chronic radiation
sickness (CRS) was introduced by A.K. Guskova, G.D. Baisogolov, et al.,
who were faced with the necessity to designate the disease developed by
several hundred workers of the Mayak facility early in the 1950s (32-34).
Accordingly, chronic radiation sickness is a complex clearly outlined syndrome
which develops as a result of a protracted exposure of the organism to
radiation with single or total doses exceed systematically the permissible
limits of occupational exposure.

It is well known that high radiation
exposure (> 1 Sv) over a short period of time (less than a day) leads to
the so-called "Acute Radiation Sickness". The Lethal 50% dose (at which
50% of the exposed persons die) varies from 3.5 Sv without intervention
to 5 Sv with medical intervention. In most countries of the world anyone
who is exposed in an accident to 0.50 Sv or more is taken off duties involving
radiation exposure or removed from residence in the accident area. But
around "Mayak" from 1949 to 1955 this was not done and many people including
workers at the reactor or plutonium extraction plant and villagers along
the Techa river received high doses for several years in succession. The
result was a disease, unique to Mayak and Techa, hereto unknown in the
worldís official disease nomenclatures. Most members of the teams visiting
the Techa villages had already gained some clinical expertise in diagnosing
and treating CRS among the Mayak workers. Nonetheless the diagnosis of
chronic radiation injury in exposed residents of the Techa River was a
difficult problem. There was no information on the levels of exposure,
and health status of the population prior to the exposure. It was difficult
to make a differential diagnosis between general somatic and radiation
pathology. It was noted that verification of the diagnoses in children
was more difficult than in adults because as a rule, children are unable
to clearly formulate their complaints.

The reports prepared in 1952-1962
initially identified 1159 cases of CRS. The disease was diagnosed in 65%
of the total adult population and in 63% of all children examined in the
village of Metlino. However, a considerable percentage (6%) of cases of
CRS were diagnosed among the residents of the lower reaches and in villages
located on the Isset River. With improved dose estimates and increased
expertise in the follow-up of exposed people, the diagnoses of CRS were
becoming better substantiated, and a proportion of diagnoses made earlier
were revised. A special commission revised the CRS diagnoses during 1959-1964
mainly based on new medical and dosimetric information in the period 1959-1964
taking into account the information contained in all available medical
and dosimetric records. The commission reported that "given the low body
content of radionuclides and in view of the fact that CRS, especially at
the first stage, has no specific symptoms, such high disease incidence
seems questionable". The diagnoses of 940 cases were considered reliable
and a dynamic follow-up was begun.

However, for reasons of military
secrecy, no mention of CRS was made in the patients' medical records and
it was forbidden to inform patients that they had CRS. A codified name
was used - ABC (astheno-vegetative syndrome) or the term "special disease"
or "specific injury". Sometimes only the stage of the disease was indicated
(stage 1 - first stage of the CRS). All of these terms were well understood
by the medical personnel of the URCRM clinic.

The main symptoms of CRS are the
changes in peripheral blood composition. It was observed that the hemoglobin
level was below 120 g/L among a considerable proportion of patients in
the early period after diagnosis of CRS as shown in fig. 10a and 10b.

a)
Men

b)
Women

Fig.10. Hemoglobin levels for exposed peoples.

The hemoglobin values which could
be interpreted as anemia (below 100 g/L for women, below 126 g/L for men)
were recorded in 26% of women and 30% of men during the period of the development
of the disease. But hemoglobin values were influenced by the inadequate
life conditions during the post-war period, imbalanced nutrition, deficient
in microelements and vitamins so that using a control group was essential.
In the period 1951-1955 patients with CRS manifested considerably reduced
thrombocyte counts as compared to controls. The distribution of thrombocyte
counts is shown in figure 11a. Leukopenia, defined as a leukocyte count
4.1x109/L and lower, was noted during the period of the development
of CRS and was most pronounced in patients with highest doses (over 1 Sv).

In some patients leukocyte counts
were in the range from 2.1x109/L to3.5x109/L during
the period of development of CRS, and is shown in figure 11b.

a)

b)

Fig.11. Levels of thrombocytes (a) and leucocytes
(b) among patients with CRS cases, exposed and control group of population.

It was also attempted to attribute
to CRS other less significant changes in the blood parameters, nervous
system, bone tissue structure, immunological resistance, miocardial functions
and gastric secretions.

The clinical symptoms described
above were mostly observed in the period characterized by external radiation
exposure, radionuclide incorporation and significant dose rates. This was
when the diagnoses of CRS were made. Later on, when the exposure of the
population to the unconfined source of radiation (river) had ceased, external
exposure stopped and internal dose rates decreased considerably. During
this latter period clinical picture was characterized by regression of
pathological symptoms and processes of gradual repair. Most patients had
recovered by the late 1960s.

None of the symptoms observed in
the patients are unique to CRS and all can be encountered in other diseases.
Therefore, a well-substantiated diagnosis of CRS had to fulfil two conditions:

(1.) Availability of clear information
on the nature of exposure and exposure dose received by the patient;

(2.) Establishment
of a differential diagnosis between radiation injury and general somatic
diseases.

Data derived from medical records
show that at the time of CRS diagnoses a large proportion of patients were
suffering from various general somatic diseases which may have manifested
symptoms imitating those of CRS. Most commonly infectious and parasitic
diseases were diagnosed, brucellosis being the most common one (149 cases).
Rural districts of Chelyabinsk region have been endemic for brucellosis
since early 1930s. Differentiation between brucellosis and radiation pathology
was always the focus of attention: the time of the occurrence and dynamics
of clinical symptoms were carefully studied, immunological methods of diagnosis
and skin tests using brucellosis vaccine were applied. The relatively small
doses received by a number of patients with CRS, and the presence of general
somatic diseases at the time of diagnosis of radiation pathology suggests
that in a number of cases the diagnosis of CRS was incorrect. At the same
time, both the verification of the individual doses and verification of
the diagnostic procedures were sufficient to conclude that at least 66
cases of CRS diagnoses were well substantiated. These cases satisfied the
main conditions for CRS verification: the rates of exposure doses accumulated
in the red bone marrow was close to 1 Sv (100 rem) for one of the exposure
years, and the period of CRS was free of other diseases with symptoms similar
to those of CRS. Note that the presence of general somatic diseases did
not preclude the development of clinical manifestations resulting from
radiation exposure, moreover, it contributed to the development of radiation
injury. Based on our experience the likelihood of the development of CRS
was higher in those patients who had developed endocrine diseases, chronic
infectious processes, avitaminosis, or reduced functions of bone marrow.
Such concurrent conditions resulted in a decrease of the organism=s
reserves, and determined, to a significant degree, the individual radiosensitivity.

The dose distribution for CRS patients
is shown in figure 12 with doses re-estimated using the best available
information..

These data contradict somewhat
statements by the International Commission on Radiological Protection (ICRP)
on chronic radiation exposure (35). The ICRP publication suggests a higher
threshold dose value for similar changes in blood caused by radiation:
0.4 Sv/y for homopiesis inhibition, 1 Sv/y for lethal bone aplasia. However,
this apparent disagreement may be based on the following:

1. The estimates of individual
doses may be and is likely to be inaccurate; 2. The proportion of CRS diagnosis
may be erroneous; 3. The threshold dose value for occurrence of non-stochastic
effects in a heterogenic population may be lower than that listed in ICRP-41
because in accidental situations the population may be exposed to a wide
range of hazardous materials and conditions, along with radiation exposure.

Some of the residents exposed on
the Techa did not develop CRS, but in the early years of exposure they
manifested isolated radiation reactions most commonly represented by hematological
changes demonstrated by peripheral blood studies.

Cancer Mortality

An increased incidence of leukemia
and other malignant neoplasms is a well-known effect of high radiation
exposure. In 1967 cohorts of exposed residents of the Techa River were
idetified by the staff of Branch No 4 of the Moscow Biophysics Institute
(now URCRM). The cohorts were defined on the basis of records from the
earlier examinations and addresses from bureau and taxation records. The
Techa River Cohort (TRC) includes 26500 people who were living in villages
on the Techa riverside (36, 37) throughout the period of the maximal releases
from 1949 through 1952 (Table 2). Their ages at the beginning of the radionuclide
releases ranged from 0 to 96 with a mean age of 29 y. About 58% of the
cohort members are women. The cohort includes two ethnic groups: Slavs
(mainly Russians) and Tatar/Bashkir. During the last decades the personal
data and residence history data for members of TRC have been updated and
corrected in accordance with newly received archival documents and personal
interviews. Later all these data were arranged in searchable form in the
MAN computer database (11,12).

The area of the follow-up of the
cohort TRC was defined to include all the territories of the five rural
districts in the Chelyabinsk and Kurgan oblasts through which the Techa
River flows. These districts include all of the contaminated villages and
all the evacuated villages. Between 1949 and 1989 almost 25% of the cohort
members are known to have left this area. Roughly 80% of the cohort members
who left the area moved to nearby cities and towns in the Chelyabinsk,
Yekaterinburg (formerly Sverdlovsk) and Kurgan oblasts. The dates and places
of migration have been obtained from address bureaus in the relevant oblast
and were included in the MAN database.

To follow-up the mortality structure
of the members of the TRC cohort the death certificates were matched manually
with the cohort roster using age, name and residence at death. Additional
information on vital status and the migration have been obtained anecdotally
during the course of clinic visits or other contacts with family members
of the cohort subjects. At the end of 1989 the vital status was unknown
for about 36% of non-migrant members of the TRC. Table 3 contains a detailed
summary of the nature of the mortality follow-up data as of the end of
1989 (37).

Table 2 Techa River Population

Exposed
in 1950-1952

Exposed
in utero and progeny of exposed parents

Exposed
since 1952

Total

Number

26,500

29,700

7,800

64,000

Table 3 Mortality Follow-up

TRC

1950-1989

Non-migrants

Migrants

Number

%

Number

%

DEAD

9,307

46

926

15

CAUSE
KNOWN

6,483

70

185

20

CAUSE
UNKNOWN

2,824

30

741

80

ALIVE

3.715

18

2,315

37

STATUS
UNKNOWN

7,175

36

3,011

48

TOTAL

20,197

100

6,288

100

TOTAL
TRC

26,485

Tables 4 and 5 summarize cases of leukemia and solid cancers for the
Techa River Cohort. In these tables the "Background" is the prediction
of the dose-response model for unexposed peoples (extrapolation to zero
dose). There were 40% excess leukemia cases. 50 were observed
compared to the 29 background cases. At doses to the red bone marrow of
over 0.50 Sv the 18 observed leukemia cases were three times the 6 background
cases. Accordingly, a statistically significant dose-dependent increase
of the leukemia mortality was observed. The number of solid cancers was
3% greater than background with an excess of 30 cases (out of 969). Similarly
an increased number of additional cases of cancer was mostly observed at
doses of over 0.5 Sv (50 rem). Excess cancer cases accounted for about
2% at doses below 0.5 Sv, and about 15% (14 cases excess over the background
of 79) at doses of over 0.5 Sv.

Table 4 Mortality from Leukemia
among Non Migrants

Red
Bone Marrow Dose, Sv

Person-years
of Observation

Background

Observed

0.005-0.10

103,031

4

3

0.10-0.20

194,858

9

13

0.20-0.50

200,144

10

16

0.50-1.00

93,873

4

9

>1.00

49,398

2

9

TOTAL

641,304

29

50

Table 5 Solid Cancer mortality
among Non Migrants

Soft-Tissue
Dose, Sv

Person-years
of Observation

Background

Observed

0.005-0.10

459,576

711

716

0.1-0.2

96,297

125

126

0.20-0.50

19,582

24

34

0.50-1.00

32,204

46

52

>1.00

33,645

33

41

TOTAL

641,304

939

969

A value for the radiation-related
carcinogenic risk was obtained in earlier studies encompassing a slightly
smaller (33 y) period of follow up (1950-1982) (36). These values
are listed in Table 6 The data at the end of 1982 (31
y follow up) were analyzed to give a risk value for for leukemia
mortality: 0.48 - 1.1 cases per 104 person-years per Sv based
upon an absolute risk model. For cancers other than leukemia (solid cancers)
the risk is based upon a relative risk model.

Table 6 Estimate of the Risk

Risk
estimates

Techa
River Cohort

Atomic
Bomb Survivors (LSS)

Leukemia
Excess absolute risk per 10,000PYSv, Linear model

0.85
(0.24-1.45)

2.94
(2.43-3.49)

All
cancer (except leukemia) Excess relative risk per Sv

0.65
(0.27-1.03)

0.41
(0.32-0.52)

Footnote: * -
90% confidence intervals given in parentheses

The linear-quadratic model for
the dependence of excess leukemia cases on accumulated dose does not fit
the leukemia data from the Techa river better than the linear model. The
absolute value of the leukemia risk for exposed members of the Techa cohort
is somewhat lower than the respective value for A-bomb survivors in Hiroshima
and Nagasaki: Life Span Study (LSS) (2.94 per 10 000 person-years per Sv).
The data on leukemia are consistent with the traditional Dose Rate Reduction
Factor (DRRF) of two to three that is used for estimating radiation risks
for continuous radiation exposure to multiply the risk deduced from LSS.
The absolute risk for solid tumors is comparable with that for A-bomb survivers
(38) but the data are not sufficient to tell whether or not the DRRF is
different from unity for these tumors also.

Thus, the calculations of excess
cancer cases based upon the data from the 33-39 y follow-up (since onset
of exposure), and the values obtained give us reason to suggest that an
extension of follow up is unlikely to result in the number of cancer cases
exceeding 200.

Possible genetic
effects

Since genetic effects following
radiation exposure might be anticipated, a study was conducted with the
aim of assessing the health status of the offspring of people exposed in
the Techa riverside villages. In particular, the unfavorable outcomes of
pregnancies, birth rate, and the mortality rate among progeny of exposed
parents are studied. No reliable effects of radiation were established.

Unfavorable outcomes of pregnancies
were studied during the period from 1956 through 1973 based on labor histories
retained at the maternity homes of the village of Mouslyumovo located on
the Techa, and of the town of Kunashak. Both exposed and unexposed women
were admitted to those maternity homes. In all, the outcomes of 2,460 pregnancies
were studied (39). The following unfavorable outcomes of pregnancies were
assessed: 1)incidence of spontaneous abortions, 2) incidence of stillbirths,
3) percentage of deaths in the early neonatal period (during the first
week of life), and 4)incidence of fatal developmental defects.

The most of the unfavorable outcomes
of pregnancies were spontaneous abortions (from 2.7 to 9.8% in different
groups: controls, with one parent exposed, with both parents exposed).
The incidence of spontaneous abortions in the control group constituted
from 2.1% to 4.2%, in when one or both parents were exposed it was estimated
to be from 3.6% to 6.1%. The rate of stillbirth was 26.2 cases per 1000
(exactly 63 cases per 2405 neonates; twin births were included in the calculations)
which is essentially higher than the respective value for the USSR in 1980
of 9.11 cases per 1000 (40). The rates of stillbirth were actually the
same for both cases with exposed parents and for controls. The coefficient
of total early neonatal mortality for all labors studied was about 2.99
cases per 1000 live birth: the respective value for children born to exposed
parents was about 4.18, and for controls it was about 1.75 cases per 1000
live births. According to the available information there were only
3 children with congenital developmental defects. These data do not allow
to draw a definite conclusion.

When both parents wereexposed the
rate of unfavorable outcomes of pregnancies was slightly lower (6.1%) than
in cases with one parent exposed (9.1%-11.7%). The rate of unfavorable
outcomes of pregnancies for controls was about 5.8%. If we assume that
a proportion of perinatal deaths can be attributed to radiation exposure
and make a comparison with the controls of the group with one parent exposed,
the doubling gonadal dose will be equal to 0.02 Sv If the doubling gonadal
dose is estimated on the basis of loss of offspring in the groups with
both parents exposed, its value will be much higher:0.42 Sv. Thus, the
range of the doubling dose is large, and the value correspondingly uncertain.
There is insufficient statistical power to draw reliable conclusions.

a)

b)

Fig.13.Birth Rate per 1,000 for control
group and exposed on the Techa River of Russian (a) and Tatar-Bashkir (b)
population in Chelyabinsk region.

An analysis of the birth rate does
not provide directly the effect of radiation exposure because of changes
in family planning practice. But birth rates do provide whether or not
the process of population reproduction has been affected in an indirect
way. They characterize the reproductive function in the exposed population.
Birth coefficients were calculated based on the registry of exposed people
and their offspring born in the period from 1950 through 1974 (41). Later
than 1974 the number of cohort members of reproductive age had decreased
considerably. By the time the presented study was completed the total offspring
included 20,278 persons representing the first-generation and 3,411 persons
representing the second-generation, i.e., in all, the progeny of parents
and grandparents exposed to radiation on the Techa River. The unexposed
population of two districts in Chelyabinsk Region (Krasnoarmeysky and Kunashaksky)
which numbered about 78,000 in the 1950s was identified as a control group.
Birth rate coefficients for controls were estimated based on data on birth
of 43,000 people in the period 1950-1974.

As shown in figures 13a and 13b,
the highest birth rate was observed in the 1950s and then decreased
throughout the follow-up period up to its end (1974). This dependence was
traced for both unexposed controls and for residents exposed on the Techa.
The negative birth trend was typical of the entire population of Russia.
It results primarily from the removal of the prohibition against abortion
and the widening scope of family planning practice. Birth rate dynamics,
shown in this study, are governed by the dependencies common to Russia
as a whole, and it indicates the correctness of these calculations. On
one hand, even if radiation affects the birth rate, it does not change
essentially the general dynamic dependencies. Also figure 13b shows that
the birth rate for the group composed of the ethnic Tatar and Bashkir population
is 1.5 times higher than that for the ethnic Russian population shown in
figure 13a. This can be attributed to different national and religious
traditions. Birth coefficients for the Tatar and Bashkir group reached
43 per 1000 in the period 1950-1959. This increase is characteristic
of families without family planning traditions, and of communities where
no contraceptives are used by women, and abortions are regarded as a serious
violation of moral principles. On the whole, the results of the study testify
to the lack of a decrease in birth rate and, accordingly, to normalcy of
reproductive function in persons whose doses to gonads ranged from 0.03
Sv (3 rem) to 1.3 Sv (130 rem).

An analysis of the death rate and of causes of death for persons assigned
to the offspring of exposed parents is an informative parameter used in
assessment of potential genetic effects of radiation exposure. Mortality
has been followed-up for 35 y since the onset of exposure and encompassed
the period from 1950 through 1984 (42). Among 1,661 death cases of offspring
of exposed parents born in 1950 and later, 1,330 cases are confirmed by
death certificates retrieved from the regional ZAGS (Civil Registrar=s
Office) archives. The analysis was made only for these cases.

The main cause of death in these
cases was disease of the respiratory organs. Infectious diseases ranked
second, and trauma third. However, the prevalence of one or other cause
of death is to a great extent dependent on age. Thus, for infectious diseases
and diseases of respiratory organs account for 62.4% of deaths among children
under 1 y, congenital anomalies, neonatal diseases and ill-defined conditions
in total account for 23.4%, and traumas for only 1.5%. For subjects aged
20 y and older, trauma ranked first among causes of death (72.6%). The
most informative parameter is infant mortality, i.e. death rate among children
under 1 y. There were 972 deaths among children under 1 y which is 58.8
% of the deaths among offspring. The most clear-cut dependence is represented
by a decrease in infant death rate, which can be traced over the period
from 1950 through the end of the study. By comparison, in Kunashaksky and
Krasnoarmeysky districts of Chelyabinsk region among the offspring of both
exposed and controls one child in ten died in the period 1950-1952 while
in 1970-1974 the death rate decreased to 15-30 death cases per 1,000. This
negative temporal trend was observed for both controls and children representing
offspring of exposed parents.

There was, however, a slight increase
in the number of deaths from endogenous causes and ill-defined conditions
among the progeny of exposed parents compared to controls. But this was
against an overall increase of the incidence of the three classes of diseases
(congenital abnormalities, diseases of neonates and ill-defined conditions).
The death rate from these causes for the offspring of exposed parents (total
groups of Slavs and Tartar-Bashkir population) made up 11.8 (5% CI:9.96-13.87),
whereas for controls the respective value was 8.22 (95% CI: 7.92-9.77),
P<0.05.

Discussion and Conclusion

Mistakes in putting into operation
the weapon-grade plutonium production plant "Mayak" caused contamination
of surrounding territories. The most serious radiation accidents involved
the release of liquid radioactive waste of the radiochemical plant directly
into the river. As a result the river ecosystem was highly contaminated
by radionuclides. It was the first tragic accident with environmental pollution
by radionuclides in human history. Experience gained in fighting its dangerous
consequences was of greathelp in later accidents in Kyshtym (1957)
and Chernobyl (1986).

About 28,000 residents of the riverside
villages accumulated doses of an average of 0.3 Sv. which significantly
exceeds allowable dose-limit for the public of 0.05 Sv. A number of villages
were evacuated. The villages on the contaminated territories, which are
still inhabited, now have additional social problems. People whose exposure
was estimated to be especially high receive social benefits. But this system
of benefits is imperfect, and many exposed people feel it leads to injustice.
This problem is now very difficult to solve, because the economic situation
in Russia is unstable.

The medical study of the exposed
population started soon after the moment of irradiation by visiting teams
of physicians. Systematic medical treatment, dose assessment and epidemiological
studies began later when a special branch of the Moscow Biophysical Institute
was organized in Chelyabinsk, which is now URCRM. Many unique materials
and findings were obtained during more than forty years of study in the
URCRM and declassified in 1990. A statistically significant excess
of 21 leukemia cases (out of 50) and a statistically insignificant excess
of 30 solid cancers (out of 969) were seen in a cohort, about half the
total population, of those permanent residents who were exposed to radiation
on the banks of the Techa River.

Data from the Techa River can address
a number of important questions, that have not been measured in humans.
These include the influence of exposure duration (dose rate) and the role
of ethnic factors. The study of the peoples exposed as a result of Techa
river contamination can provide unique contributions to the knowledge of
the impact of radiation on humans and hence on radiation protection and
safety.

Acknowledgements: This
review, as with all reviews, would not have been possible without the extensive
work and the approval of many people. Dmitry Burmistrov would like to thank
the Richard Lounsbury Foundation and Harvard University for generous support.
He is grateful to Dr. Marina Degteva, Dr. Nelli Safronova and Dr. Eugeniya
Tolstykh for printed materials related to this review, and Dr. Elena Shihkina
for her assistance. Mira Kossenko wishes to thank Dr. Angelina Guskova
for extremely useful discussions on diagnostic of Chronic Radiation Sickness,
and Dr. Dale Preston for his help in analysis of stochastic effects in
the Techa River Cohort. Richard Wilson would like to thank the UCRM for
their hospitality on many occasions. Many of the reviewed studies were
supported by the U.S. - Russian Joint Coordinating Committee on Radiation
Effects.

References

1Joint
Norwegian-Russian Expert Group for Radioactive Contamination in the Northern
Areas, Sources Contributing to Radioactive Contamination of the Techa
River and Areas Surrounding the Mayak Production Association, Urals, Russia
(October 1997).

11M.O.
Degteva, V.P. Kozheurov, M.I. Vorobiova, "General Approach to Dose Reconstruction
in the Population Exposed as a Result of the Release of Radioactive Wastes
into the Techa River", Sci. Total Environ, 142: 49-62 (1994).

21V.P.
Kozheurov, "SICH-9.1- A Unique Whole-body Counting System for Measuring
90Sr via Bremsstrahlung: the Main Results from a Long-term Investigation
of the Techa River Population", Sci. Total Environ, 142(1-2): 37-48
(1994).

23V.P.
Kozheurov, M.O. Degteva "Dietary Intake Evaluation and Dosimetric Modelling
for the Techa River Residents Based on in vivo Measurements of Strontium-90
in Teeth and Skeleton", Sci. Total Environ., 142: 63-72 (1994).

34N.D.Okladnikova,
V.S.Pesternikova, M.V.Sumina, V.N.Doshchenko. "Occupational Diseases from
Radiation Exposure at the first Nuclear Plant in the USSR". The Science
of the Total Environment 142 9-17 1994 (in Russian)